Mom's Prenatal Smoking Tied to Kids' Obesity

by Michael Smith Michael Smith North American Correspondent, MedPage Today
September 04, 2012

Action Points

Children whose mothers smoked during pregnancy are at increased risk of obesity when they reach adolescence, and a key factor appears to be subtle changes in the brain's reward mechanism.

Point out that a lower volume of the amygdala was found among adolescents whose mothers smoked during pregnancy.

Children whose mothers smoked during pregnancy are at increased risk of obesity when they reach adolescence – and a key factor appears to be subtle changes in the brain's reward mechanism, researchers reported.

In a cohort of adolescents, those whose mothers smoked during pregnancy had higher body fat (P=0.009) and fat intake (P=0.001) than offspring of nonsmokers, according to Zdenka Pausova, MD, of the Hospital for Sick Children in Toronto, and colleagues.

They also had lower volume in the amygdala (P<0.001), which is part of the brain's reward processing system, Pausova and colleagues reported online in Archives of General Psychiatry.

"Prenatal exposure to maternal cigarette smoking is a well-established risk factor for obesity," Pausova and colleagues noted, "but the underlying mechanisms are not known."

A preference for fatty foods -- regulated at least in part by the brain's reward system -- might play a role, they hypothesized.

To test the idea, they turned to the ongoing Saguenay Youth Study, which includes people drawn from the genetic founder population of the Saguenay Lac St. Jean region of the Canadian province of Quebec, a group characterized by relatively high genetic and cultural homogeneity.

The study population included 378 teens, ages 13 to 19, with Tanner stage 4 and 5 sexual maturity. Of those, 180 had been exposed to prenatal maternal smoking that, on average, amounted to about 11 cigarettes a day during all three trimesters.

The researchers analyzed fat intake (using a food recall questionnaire), body fat percentage, and (using magnetic resonance imaging) the volume of three structures involved in reward processing, the amygdala, the nucleus accumbens, and the orbitofrontal cortex.

They found that, compared with the non-exposed participants, those exposed to prenatal maternal smoking had:

Higher total body fat, on average. The difference -- approximately 1.7 kg or 3.7 lbs – was significant at P=0.009.

Higher fat intake as a percentage of total energy intake. The difference was 2.7% and was significant at P=0.001.

Lower amygdala volume, by 95 cubic millimeters, which was significant at P<0.001, although there was no significant difference in the other two brain structures.

Consistent with a possible role in limiting fat intake, the researchers reported, amygdala volume was inversely correlated with fat intake, at r=−0.15, which was significant at P=0.006.

Interestingly, Pausova and colleagues wrote, only about half of the exposed participants had lower amygdala volume and higher fat intake – those with a body mass index above the median.

That suggested, they argued, that other factors – possibly genetic – might be protecting some participants from the effects of maternal smoking.

Fatty foods are regarded as very rewarding, the researchers noted, with effects that in some experiments resemble those of drugs of abuse.

So, Pausova and colleagues argued, the well known link between prenatal exposure to maternal smoking might promote obesity by enhancing dietary preference for fat.

"This effect may be mediated in part through subtle structural variations in the amygdala," they concluded.

The study had support from the Canadian Institutes of Health Research, the Heart and Stroke Foundation of Quebec, and the Canadian Foundation for Innovation.

The journal said the researchers made no financial disclosures.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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